Radar data compression system and method

ABSTRACT

A radar system includes a controller equipped with memory for storing data. The controller is configured to receive a time-domain signal representative of a reflected signal detected by an antenna, and transform the time-domain signal into a plurality of range datasets. Each range dataset corresponds to one of the plurality of chirps, each range dataset is represented by a series of values assigned to a plurality of range bins, and each of the values includes a sign bit. The controller is also configured to compress the plurality of range datasets by storing in the memory a portion of each of the values assigned to at least one of the plurality of range bins, wherein the portion is defined to exclude a first number of redundant sign bits of each value. The controller may further compress the portion by retaining a second number of bits of the data by excluding some of the least significant bits of each value.

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to radar signal processing, and moreparticularly relates to compressing radar data.

BACKGROUND OF INVENTION

It is known that radar systems using a Fast Chirp Waveform to emit aradar signal often accumulate large amounts of processed data in memoryas arrays of data produced by a Range Fast Fourier Transform (FFT) and aDoppler FFT. The memory size depends on a variety of system parameters,but it is not uncommon for up 10,000,000 bytes (10 MB) to be temporarilystored. To minimize system cost, it is desirable to reduce the amount ofmemory necessary to implement a Fast Chirp Waveform.

SUMMARY OF THE INVENTION

Described herein is a system and method for radar data compression thatreduces the amount of data that needs to be accumulated between theRange FFT and the Doppler FFT in a radar system using a Fast ChirpWaveform.

In accordance with one embodiment, a radar system is provided. The radarsystem includes an antenna and a controller. The antenna is configuredto detect a reflected signal characterized as a reflection of an emittedsignal reflected by an object present in a field-of-view 18 of theantenna. The emitted signal includes of a plurality of chirps. Thecontroller is equipped with memory for storing data. The controller isconfigured to receive a time-domain signal representative of thereflected signal detected by the antenna. The controller is alsoconfigured to transform the time-domain signal into a plurality of rangedatasets. Each range dataset corresponds to one of the plurality ofchirps. Each range dataset is represented by a series of values assignedto a plurality of range bins. Each of the values includes a sign bit.The controller is also configured to compress the plurality of rangedatasets by storing in the memory a portion of each of the valuesassigned to at least one of the plurality of range bins. The portion isdefined to exclude a first number of redundant sign bits of each value.

In another embodiment, a method of radar data compression is provided.The method includes providing a memory for storing data; receiving atime-domain signal representative of a reflected signal detected by anantenna. The reflected signal arises from an emitted signal thatincludes of a plurality of chirps. The method also includes transformingthe time-domain signal into a plurality of range datasets. Each rangedataset corresponds to one of the plurality of chirps. Each rangedataset is represented by a series of values assigned to a plurality ofrange bins. Each of the values includes a sign bit. The method alsoincludes compressing the plurality of range datasets by storing in thememory a portion of each of the values assigned to at least one of theplurality of range bins, wherein the portion is defined to exclude afirst number of redundant sign bits of each value.

In yet another embodiment, the plurality of range datasets is furthercompressed when portion is further defined to retain a second number ofbits of the data by excluding least significant bits of each value.

Further features and advantages will appear more clearly on a reading ofthe following detailed description of the preferred embodiment, which isgiven by way of non-limiting example only and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a top view of a vehicle equipped with a radar system,according to one embodiment;

FIG. 2 is a block diagram of the system of FIG. 1, according to oneembodiment;

FIG. 3 is a waveform diagram of a signal emitted by the system of FIG. 1in accordance with one embodiment;

FIG. 4 is an illustration of a data array present in the system of FIG.1 in accordance with one embodiment;

FIG. 5 is an illustration of a data array present in the system of FIG.1 in accordance with one embodiment;

FIG. 6 is an illustration of a data field present in the system of FIG.1 in accordance with one embodiment; and

FIG. 7 is a flowchart of a method performed by the system of FIG. 1 inaccordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a non-limiting example of a vehicle 10 equipped witha radar system, hereafter the system 20. The system 20 is illustrated asbeing located in an interior compartment of the vehicle 10 behind awindow 12 of the vehicle 10. While an automobile is illustrated, it iscontemplated that the system 20 is also suitable for use on othervehicles such as heavy duty on-road vehicles like semi-tractor-trailers,and off-road vehicles such as construction equipment. In thisnon-limiting example, the system 20 is located behind the windshield andgenerally forward of a rearview mirror 14. Alternatively, the system 20may be positioned to ‘look’ through a side or rear window of the vehicle10, or be located proximate to a front or rear bumper of the vehicle 10.

The system 20 is generally configured to detect one or more objects(e.g. the object 16) relative to the vehicle 10. Additionally, thesystem 20 may have further capabilities to estimate the parameters ofthe detected object(s) including, for example, the object position andvelocity vectors, target size, and classification, e.g., vehicle versespedestrian. The system 20 may be employed onboard the vehicle 10 forautomotive safety applications including adaptive cruise control (ACC),forward collision warning (FCW), and collision mitigation or avoidancevia autonomous braking and lane departure warning (LDW).

FIG. 2 further illustrates non-limiting details of the system 20. Thesystem 20 may include an antenna 22 configured to detect a reflectedsignal 24 characterized as a reflection of an emitted signal 26reflected by an object 16 in a field-of-view 18 of the antenna 22. Anexample of the field-of-view 18 is generally defined by the dashed linesillustrated in FIG. 1.

FIG. 3 illustrates a non-limiting example of the emitted signal 26 as agraph of frequency 30 versus time 32. The emitted signal 26 generallyincludes of a plurality of chirps 34. Each of the plurality of chirps 34is characterized as a sweep of the frequency of the emitted signal 26from a first frequency 36 (f1) to second frequency 38 (f2) during achirp interval 40 (τ) which defines a chirp slope 42 (−S). Each of theplurality of chirps 34 is spaced apart from a prior or subsequent chirpby a silent interval 44 (τ_(s)). A sequence of K chirps are emitted overa time interval 46 (t_(d)) to form the emitted signal 26, which issometimes called a Fast Chirp Waveform. By way of further example andnot limitation, suitable values for these variables include a firstfrequency 36 of 76.55 Giga-Hertz (GHz), a second frequency 38 of 76.45GHz, a chirp interval 40 of 100 microseconds (us), a chirp slope 42 of 1Mega-Hertz per microsecond (MHz/us), a silent interval 44 of 10 us, achirp count 48 (K) of 64 chirps which results in a time interval 46 of7040 microseconds (us). The silent interval 44 is selected so that todetermine the total time interval between the start of one chirp and thestart of a subsequent chirp.

Referring again to FIG. 2, the system 20 includes a controller 50. Thecontroller 50 may include a processor 52 such as a microprocessor orother control circuitry such as analog and/or digital control circuitryincluding an application specific integrated circuit (ASIC) forprocessing data as should be evident to those in the art. The controller50 may include memory 54, including volatile memory such as SDRAM, andor including non-volatile memory such as electrically erasableprogrammable read-only memory (EEPROM) for storing one or more routines,thresholds and captured data. The one or more routines may be executedby the processor 52 to perform steps for determining if signals receivedby the controller 50 indicate the presence of an object 16 in thefield-of-view 18. The controller may also include a transmitter 56 and areceiver 58 for coupling the antenna 22 to the processor 52 as will berecognized by those in the art.

As described above, the controller 50 is equipped with memory 54 forstoring data such as samples of signals output by the receiver 58 whichcorresponds to the reflected signal 24. As such, the controller 50, ormore specifically the processor 52, is configured to receive atime-domain signal 60 representative of the reflected signal 24 detectedby the antenna 22. The receiver 58 may include amplifiers and filters tocondition the signal from the antenna 22 to be suitable for theprocessor 52. The processor 52 may include an analog to digitalconverter or ADC (not shown) configured to sample the time-domain signal60. A suitable ADC would have a resolution of 12 bits and be operable ata sample rate of 5 million samples per second.

FIG. 4 illustrates a non-limiting example of a first array 100 of data,where each cell 102 of the first array 100 represents a memory locationthat contains a numerical value indicative of the time-domain signal 60at the moment it was sampled. The time-domain signal 60 is sampledsynchronously with the emitted signal 26 so that the reflected signal 24corresponding to each chirp is sampled a sample count 104 (M) number oftimes. That is, each cell 102 of the first array 100 is loaded with anumerical value starting at the bottom left corner of the first array100 and going up the first column until ‘M’ samples are collected, andthen the next column is filled bottom to top. There may be wait timebetween the ‘Mth’ sample of one column and the first sample of asubsequent column based on the silent interval 44 (FIG. 3). By way ofexample and not limitation, a suitable number of samples (i.e. the valueof ‘M’ in FIG. 4) is 1000 samples.

FIG. 5 illustrates a non-limiting example of a second array 200 of datathat arises by performing a Fast Fourier Transform (FFT) on data storedin the first array 100, which is sometimes referred to as a Range FFT.Each column of data in the first array 100 represents a time-basedsampling of the time-domain signal 60 for duration comparable to thechirp interval 40. The Range FFT transforms the time-based sampling intothe range domain so that each cell 202 in the second array 200 containsa numerical value indicative of the magnitude of the reflected signal 24for a particular range bin 208. As such, the controller 50 is configuredto transform the time-domain signal 60 into a plurality of rangedatasets 206, wherein each of the range datasets 206 (i.e. each columnof the second array 200) corresponds to one of the plurality of chirps34. That is, each vertical column of the second array 200 is a rangedataset 206 that provides an indication of the magnitude of thereflected signal 24 corresponding to a particular range from the antenna22.

Each range dataset (i.e. each column) is represented by a series ofvalues, typically complex values, assigned to a plurality of range bins.For example, the second range bin (row 2) may suitably correspond to adistance or range from the antenna 22 of 1.5 meters (m)+/−0.75 m, andthere may be 100 range bins so the range bin count 210 (i.e. the Nthrange bin) may suitably correspond to a distance or range from theantenna 22 of 150 m+/−0.75 m. There may be data available for distancesor ranges greater than the Nth range bin, but that data is discarded andnot stored in the second array 200.

FIG. 6 illustrates a non-limiting example of a format of a data field220 stored in a cell 202 of the second array 200. By way of example andnot limitation, the data field may be 32 bits (e.g. a 16-bit complexvalue) The numerical values in each cell 202 are stored in2's-compliment form and are right-justified within the data field 220 ofeach cell 202. As such, each of the values includes one or more signbits 222 (S-bits). Small magnitude positive values will have multiplerepeated zeroes (0's) to the left of a value portion 224 of the datafield 220, and small magnitude negative values will have multiplerepeated ones (1's) to the left of the value portion 224 of the datafield 220. These multiple repeated 0's or 1's are generally redundantand the duplicates can be discarded without changing the value beingstored. By discarding a first number of the redundant bits of the signbits 222, the data can be compressed so that the amount of memorynecessary to store the second array 200 can be reduced.

It is recognized that the first number of the sign bits 222 discardedwould need to be tracked, and that if the first number of sign bits 222was tracked for each cell 202 on an individual basis, there would likelynot be a significant amount or degree of compression realized. However,if the second array 200 were segregated in to sections or portions, andthe first number of sign bits discarded were held constant across theentirety of a particular portion of the second array 200, then asubstantial degree of compression could be realized.

How the second array 200 could be segregated into portions for thepurpose of discarding a fixed number of the sign bits 222 could bedetermined by searching for portion boundaries where all the data withina portion boundary has a magnitude less than or greater than somethreshold. Alternatively, since it is expected that the generalmagnitude of the values stored would be similar across a particularrange bin (i.e. relatively constant across a particular horizontal rowof the second array 200), the first number of the sign bits 222discarded could be held constant across a range bin 208. Then only onenumber of the sign bits 222 discarded for each particular range bin(each row) would need to be stored. In other words, the first number ofredundant sign bits excluded could be varied or selected according tothe maximum magnitude of the values assigned to a particular range binacross all of range datasets. That is, the first number of redundantsign bits excluded from a particular horizontal row of the second array200 would be determined based on the maximum magnitude of the dataoccurring in that particular row. By this technique, the controller 50is configured to compress the plurality of range datasets 206 by storingin the memory 54 a portion (e.g. the value portion 224 and at least oneof the sign bits 222) of each of the values assigned to at least one ofthe plurality of range bins 208, wherein the portion is defined toexclude a first number of redundant sign bits of each value.

Since the resolution of data from relatively large magnitude signals maybe more than is necessary for the system 20 to reliably detect theobject 16 (or multiple objects), it may be advantageous if the pluralityof range datasets 206 is further compressed if the portion of the datafield 220 is further defined to retain a second number of bits of thedata by excluding some of the least significant bits 226 (Q-bits) ofeach value. The second number of data bits retained, with exclusion ofredundant sign bits and remaining LSBs, will then determine theperformance achievable in subsequent processing of the compressed data.If there are some range bins where greater than typical accuracy isdesired, then some range bins may store more bits than others. However,for simplicity of memory management, it may be preferable to alwaysstore the same number of bits in each cell 202 for the entirety of thesecond array 200, for example eight bits.

The data being compressed is from the output of the Range FFTs. Afterall of the Range FFTs have been processed, the data from one range binfor each of the Range FFTs will be arranged into a single vector. ADoppler FFT will then be performed across that vector. This willdetermine the Doppler value of an object within that particular rangebin. The number of bits stored determines the level of accuracy that canbe achieved in subsequent processing of a Doppler FFT. As such, thenumber of bits stored or retained is preferably determine a priori aspart of the design of the compression strategy, keeping in mind thatincreasing the bits retained provides for increased dynamic range in asubsequent Doppler FFT, but degrades the compression ratio.

If there is more than one object within that range bin, then multipleobjects can be detected. One important consideration is the ability todetect a small object in the range bin given the presence of a largerobject in that same range bin. The Doppler FFT process has somerequirements as to the dynamic range of the measurement. It is desirableto identify multiple signals of varying amplitudes within this DopplerFFT. Supposing that the signals from two objects differ in amplitude by,for example, 30 dB. To distinguish these to objects, the dynamic rangeof the output needs to be maintained to better than 30 dB. If thedynamic range is less than 30 dB in the FFT, it may not be possible todistinguish the smaller signal in the Doppler FFT output from the noisegenerated by the larger signal. As such, the dynamic range of theDoppler FFT will be generally limited by the number of bits of the inputdata retained. This is because the data is quantized at X bits below thepeak signal. This quantization noise can mask smaller objects.Therefore, the number of bits stored in this compression sets thedynamic range that can be achieved within the Doppler FFT.

There are general limits as to how much dynamic range is important inthe Doppler FFT. Based on various design decisions (such as theside-lobe level of the FFT response from the larger object), signalsmore than some level below the largest signal in the range bin may be ofno concern. If, for example, this level is 40 dB, then keeping a numberof bits that result in more dynamic range in the Doppler FFT than isuseful is unnecessary. If, for example, retaining 7 bits in thecompression routine is sufficient to provide 40 dB dynamic range in theresulting Doppler FFT, then saving more than 7 would be unnecessary, andwould degrade the compression ratio. Accordingly, a certain minimumnumber of bits are retained to protect the dynamic range that can beachieved in the resulting Doppler FFT, so that no more bits than arenecessary are retained to achieve a high compression ratio.

A third array (not shown) may be produced that is a one-dimensionalarray, i.e. a single column or row of data, by performing a subsequentFast Fourier Transform (FFT) on data stored in the second array 200,which is sometimes referred to as a Doppler FFT. Each horizontal row ofdata in the second array 200 (e.g. row ‘n’) represents a sample of thereflected signal 24 for a particular range. A Doppler FFT transforms therange domain into the Doppler domain so variation in the magnitude ofthe range domain over time can be evaluated to detect relative motion ofthe object 16 relative to the antenna 22. The teachings about datacompression described above can also be used to compress data producedby the Doppler FFT.

FIG. 7 illustrates a non-limiting example of a method 700 of radar datacompression. Compressing radar data is advantageous as it reduces theamount of memory that a radar system (e.g. the system 20) must beequipped with to handle processing of radar signals (e.g. thetime-domain signal 60)

Step 710, PROVIDE MEMORY, may include providing or equipping thecontroller 50 with a memory 54 such as random access memory (RAM) forstoring data captured or generated by the processor 52.

Step 715, TRANSMIT CHIRP AND DETECT REFLECTED SIGNAL, may includeoperating the transmitter 56 to transmit the emitted signal 26 thatincludes a plurality of chirps 34, and operating the receiver 58 toreceive a signal corresponding to the reflected signal 24 detected by anantenna 22. Those in the art will recognize that the reflected signal 24arises from the emitted signal 26 that includes of the plurality ofchirps 34. Step 715 may also include operating the receiver 58 in orderto generate the time domain signal which corresponds to, or isrepresentative of, the reflected signal 24.

Step 720, RECEIVE TIME-DOMAIN SIGNAL, may include the processor 52capturing or receiving the time-domain signal 60 which, as noted before,is representative of a reflected signal 24. Step 720 may includeoperating an analog-to-digital converter or ADC (not shown) within theprocessor in order to capture digitized samples of the time-domainsignal 60. These digitized samples may be stored in the memory 54, andmay be organized in the memory 54 so as to be accessible in either arow-wise or column-wise manner similar to that suggested by the firstarray 100.

Step 725, FFT TIME-DOMAIN SIGNAL, may include transforming the digitizedsamples that correspond to the time-domain signal 60 stored in the firstarray 100 into a plurality of range datasets 206 which may be stored inthe memory 54 and organized in a manner similar to that suggested by thesecond array 200. Each of the range datasets 206 corresponds to one ofthe plurality of chirps 34 as each range dataset is represented by aseries of values assigned to a plurality of range bins where the valuescorrespond to the strength or magnitude of the reflected signal for aparticular distance from the antenna 22. The values stored in the cells202 of the second array 200 are preferable stored as a 2's-complementbinary value, so each of the values includes at least one sign bit, andas it the convention for a 2's-complement binary value, may include oneor more redundant sign bits if the magnitude of the value storedrequires less than the maximum number of bits available in each of thecells 202.

Steps 730-745 are associated with the unnumbered step COMPRESS RANGEDATASETS. In general, compressing the plurality of range datasetsarising from the FFT of the time-domain signal 60 is accomplished bystoring in the memory 54 a portion of each of the values assigned toeach of the plurality of range bins. In general, the portion is definedto exclude redundant sign bits from the sign bits 222, and optionallyexclude some of the least significant bits 226.

Step 730, DETERMINE MAXIMUM MAGNITUDE, may include searching all of thevalues stored in the range bin 208 for the maximum positive or negativemagnitude value so that the first number of redundant sign bits excludedis the same for all of the values stored in a particular range bin. Thatis, it may be preferable to exclude the same number of redundant bitsacross a particular range bin even if that means that some of the valuesin the particular range bin still have some redundant sign bits.Otherwise, if the first number of redundant sign bits excluded variedacross the range bin, then that variation would need to be accounted forso the compression factor would likely be reduced.

Step 735, EXCLUDE REDUNDANT SIGN BITS, may include storing only theportion of the data field 220 necessary to retain the value portion 224and at least one of the sign bits 222. It may be advantageous if thefirst number of redundant sign bits excluded is varied or selected inaccordance with a maximum magnitude of the values assigned to aparticular range bin across the plurality of range datasets. That is,the first number of sign bits excluded for a particular range bin may beconstant, but the first number of sign bits excluded for some otherrange bin may be different depending on the maximum magnitude detectedin that other range bin.

Step 740, DETERMINE RESOLUTION, may include recalling from memory apredetermined resolution value, or dynamically determining a desiredresolution based on the content of the time-domain signal 60. Forexample, if prior passes through the object detection process suggestedthat the object 16 was not a single target but include multiple targets,or that the location of object 16 was not determined with a high degreeof confidence, then the resolution may be temporarily increased tobetter assess the object 16. However, in order to keep the management ofthe memory 54 simple, it may be preferable if the resolution was alwaysheld constant so the size of the portion is defined such that apredetermined number of bits are stored in each range bin.

Step 745, EXCLUDE LEAST SIGNIFICANT BITS, may include excluding some ofthe least significant bits 226 so that a second number of bits retainedand stored is a constant. If the value portion 224 has a relativelylarge number of bits, then some of the least significant bits 226 may beexcluded without sacrificing accuracy. That is, the plurality of rangedatasets 206 may be further compressed when the portion is furtherdefined to exclude some of least significant bits 226 of each value.

Step 750, STORE COMPRESSED RANGE DATA, may include the processor 52storing into the memory 54 the contents of the second array 200 forfuture use. For example, the transmitting of the plurality of chirps 34in the emitted signal 26 and the detecting/receiving of the reflectedsignal 24 may be repeated multiple times in order to increase theoverall signal to noise ratio for more confidently determining thelocation and/or relative motion of the object 16.

Step 755, ALL CHIRPS TRANSMITTED?, may include comparing the number ofchirps transmitted to the value of the chirp count 48. If not all of theplurality of chirps 34 have been transmitted, the method 700 returns tostep 715. If all of the chirps have been transmitted, the method 700proceeds to step 760. It is recognized that some of the steps performedwithin the processing loop defined by steps 715 to 750 may be doneoutside of a loop that transmits the emitted signal 26 and detects thereflected signal 24 if the speed if the processor 52 is lacking.However, performing the steps within the defined loop as presented ispreferred as it generally provides increased memory efficiency.

Step 760, FFT RANGE DATA, may include applying a FFT to each of rangebin 208 in order to determine an indication of relative motion betweenthe antenna 22 and the object 16

Step 765, STORE DOPPLER DATA, may include compressing the data from step760 using similar techniques for excluding redundant sign bits andlimiting the resolution as describe above with regard to the secondarray 200.

Step 770, DETECT OBJECT, may include searching the stored data forpatterns that indicate various characteristics of the object 16 or otherpotential objects in the field-of-view 18 such as size, location, andmotion relative to the vehicle 10.

Accordingly, a radar system (the system 20), a controller 50 for thesystem 20 and a method 700 of radar data compression is provided. Thereare multiple ways that the data processing describe herein can beperformed. For example, the controller 50 may collect all time-domainsamples, and then perform a 2-D FFT. Alternatively, the controller 50may process the Range FFT as the data is acquired, and then perform theDoppler FFT after the full look is acquired. Regardless of the exactorder of steps, it is necessary to collect the samples from all of thechirps into a relatively large memory buffer before the Doppler FFT canbe performed. This is because the Doppler FFT requires data from allchirps before significant processing can be performed.

The size of the memory 54 is determined by various design factors, butit generally holds that an increased memory size is required for ahigher resolution (e.g. higher performance) measurement for a given setof range, Doppler coverage parameters. Because memory (e.g. RAM) is arelatively expensive component of a radar system, it is advantageous toreduce the amount of RAM required for a given design. Other types ofcompression such as lossless compression algorithms used on data similarto that found in a radar system typically do not achieve highcompression ratios.

Described herein is a compression technique is to save the minimumnumber of bits per value to ensure data is retained to an adequatedynamic range. The dynamic range of the data (or smallest amplitudesignals of interest relative to the largest in the signal) willdetermine the second number of bits required to be retained. The datathat is collected has various factors that drive dynamic range. Thedifference in the Radar Cross Section (RCS) of objects that needs to bemeasured. The RCS is an object parameter which indicates the signal thatwill be reflected from an object back toward the radar. Typically,automotive radars have an interest in objects from perhaps 40 dB squaremeters (dBsm) to −20 dBsm. The signal amplitude received from an objectvaries with 1/range⁴, which means that objects with the same amplitudewill have large signal level differences with range. This means that anobject's signal level will vary with 40*log(range_(ref)/range).

The signal amplitude received at the antenna of the radar is typicallyfiltered to manage the signal amplitude received at the ADC. Thisbaseband filter response is typically used to counteract the 1/range⁴signal dependence, along with rejecting various leakage and biascomponents of the radar system. Other minor factors can exist, but theseare the primary drivers for a single receive channel. As the Range FFTand Doppler FFT are performed, they will achieve a Signal to Noise (SNR)gain, which has the effect of increasing the desired dynamic range ofthe output signal compared with the input signal. The incoming data willpreferably be processed through the end of the Range FFT withoutcompression. This is done as the data is being received, one chirp at atime, without being stored in a buffer to receive all incoming ADC data.The data to be stored will be the X most significant bits of data aftersome redundant sign bits are removed. For clarification, values aretypically represented as right-justified within a data field. Smallpositive values will have multiple zeroes to the left of the value.Small negative values (stored in 2's complement) will have 1's to theleft of these values. These bits are referred to as redundant and can bediscarded without changing the value being stored.

For compression, X bits per location, where X is constant across theentire memory buffer. Selection of X is based upon the dynamic rangeneeding to be achieved through the second stage FFT. The first number ofsign bits discarded will be constant over some range of the memorybuffer, to prevent the need to store this first number individually foreach location. The first number of sign bits needs to be stored in somemanner so that the data can be restored when being decompressed. Becausethe data that is to be stored from one chirp must be compressed beforethe signals from all chirps are known, only the data available prior toand including that chirp can be used for determining sign bits. Thiscompression approach will determine the first number of sign bits to bediscarded (“S”) independently for each Range bin.

After the Range FFT, signals from objects at different ranges havealready been separated into different bins. By limiting consideration ofS to a single range bin, two factors which drive dynamic rangerequirements are eliminated, namely the 1/R⁴ dependence of the signal onrange and the frequency response of the baseband signal chain. Once allof the chirps have been collected, the largest signal within a range binwill determine the minimum value of S that can be used within the rangebin. Although the signal amplitude may be relatively constant within arange bin across chirps, values later in the sequence may have fewerredundant sign bits than assumed previously in the sequence.

This approach will use a value of S equal to the minimum of the largestvalue possible in the current chirp and the minimum value used in allprevious chirps. In this manner, the value of S can change across thechirps, but only downward as the chirps are transmitted. Later chirpswill not have a larger value of S than earlier ones within a range bin.This approach is a strategy to reduce the information needed to recordwhich bits are stored within the range bin. Recorded data only needs toinclude initial S value and chirps in which the S value changes

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A radar system comprising: an antenna configured to detecta reflected signal characterized as a reflection of an emitted signalreflected by an object present in a field-of-view of the antenna,wherein the emitted signal includes of a plurality of chirps; and acontroller equipped with memory for storing data, said controllerconfigured to receive a time-domain signal representative of thereflected signal detected by the antenna, transform the time-domainsignal into a plurality of range datasets, wherein each range datasetcorresponds to one of the plurality of chirps, each range dataset isrepresented by a series of values assigned to a plurality of range bins,and each of the values includes a sign bit, and compress the pluralityof range datasets by storing in the memory a portion of each of thevalues assigned to at least one of the plurality of range bins, whereinthe portion is defined to exclude a first number of redundant sign bitsof each value.
 2. The system in accordance with claim 1, wherein thefirst number of redundant sign bits excluded is varied in accordancewith a maximum magnitude of the values assigned to a particular rangebin across the plurality of range datasets.
 3. The system in accordancewith claim 1, wherein the plurality of range datasets is furthercompressed when the portion is further defined to retain a second numberof bits of the data by excluding least significant bits of each value.4. The system in accordance with claim 1, wherein the portion is definedsuch that a predetermined number of bits are stored in each range bin.